Besides files I would like to mark folders as favorites. For example, I have a folder represening a book with the book title as folder name. Within the folder I store different editions of this book (3rd Edition.pdf, 4th Edition.pdf, ...). It makes no sense to mark each PDF as favorite.

In connection with the 1. feature request, where folders represent books, it would be helpful to switch off placing folders before files. Instead it should be possible to sort folders and files equally, like on Mac OS, i.e.: